The invention relates to a centrifuge and to a method for monitoring a torque.
Centrifuges which are used for the processing of drill sludge are known. In the processing of such sludge, also called drilling mud, a centrifuge is usually operated at a lower load than in the processing of other products. One reason for this is that, in the event of failure because of overloading, complicated demounting and cleaning of the centrifuge have to be carried out.
DE 10 2006 028 804 A1 discloses a generic centrifuge with a drum and with a screw which are driven by a first motor and preferably a second motor. A gear arrangement which has a plurality of gear stages is arranged between the motors and the drum and screw. Torques are introduced into the first and the second gear stage on four shafts, and a first and a second gear stage is driven on at least three shafts. The arrangement serves, inter alia, for generating a differential rotational speed between the drum and screw.
In a design variant, in DE 10 2006 028 804 A1, an unregulated drive is implemented in which a gear input shaft is detained. In this context, the possibility of implementing torque overload protection on the stationary shaft is described.
DE 94 09 109 U1 discloses a centrifuge with two epicyclic gear stages, combined into a synchronized gear. In one of the design variants explained, an input of the epicyclic gear stages is detained and a signal is determined at this input as a function of the torque at the screw. This signal can be used for monitoring, overload indication and/or damping measures.
FR 81 11 786 discloses a solid bowl screw centrifuge with a torque overload protection device having a lever which is held on a jib of a gear input shaft via intermediate elements. A lever end is held between two running rollers which are connected to a spring support via a double-jointed arm. In this case, when the centrifuge is in operation, the lever presses against one of the two running rollers which is connected to a measuring instrument. This measuring instrument determines the force exerted by the lever and, when a predetermined limit value is overshot, outputs a control command to a centrifuge control device which stops the inflow of product into the centrifuge. In the event of too high an overload, the double-jointed arm can collapse, the fixing of the lever being released by the running rollers. The gear input shaft of the centrifuge is thus no longer fixed or is released.
The object of the invention is to provide a centrifuge which makes it possible to process drill sludge, as product, in an especially suitable way.
The invention achieves this and other objects by providing a solid bowl screw centrifuge with a rotatable drum and with a rotatable screw for the processing of drill sludges. The centrifuge has a drive device for driving the drum and the screw, with a drive motor and with a gear arrangement for generating a differential rotational speed between the drum and the screw during the operation of the centrifuge. A gear input shaft of the gear arrangement is rotationally fixed by an overload lever arm that is triggerable in a torque overload event. The overload lever arm, spaced apart at one end radially with respect to the axis of rotation of the gear input shaft, is releasably connected directly to the gear input shaft or to a part connected thereto in a rotationally fixed manner.
The invention further achieves this and other objects by providing a method for monitoring the torque on a gear input shaft of a solid bowl screw centrifuge in the clarification of drill sludge. The method includes the following steps: (a) clarification of drill sludge if the torque or the solid bowl screw centrifuge is below a first limit value; (b) changing of at least one operating parameter of the solid bowl screw centrifuge if the torque reaches or overshoots the first limit value; (c) shutdown of the solid bowl screw centrifuge if the torque reaches or overshoots a second limit value; and (d) automatic or controlled triggering of torque overload protection if the derivation of the torque according to time overshoots a limit value dM/dt.
As a result of the special configuration of the overload lever arm and its connection to the gear input shaft, structural simplification, as compared with the prior art, is achieved.
The overload lever arm in this case serves advantageously as a torque support which, in the event of overload, comes loose from the gear input shaft or from the part, such as an arm or pulley, connected fixedly in terms of rotation to it.
In this context, “a normal operation” means that the torque acting upon the overload lever arm is lower than a stipulated first limit value. When this first limit value is overshot, operating parameters are first modified in a suitable way. Thus, for example, the product inflow can be throttled.
If a second, higher limit value for the torque is overshot, the solid bowl screw centrifuge is shut down and assumes a safe state.
The term “overload event” means that the torque rises to an extent such that compensation by the influencing of process parameters and even a shutdown can no longer take place in due time. In this case, the overload lever arm is compressed. As a result, the gear input shaft is released and the belt drive of the motor can no longer transmit torque via the gear to the screw or the drum.
The overload lever arm is preferably designed as a cylinder/piston arrangement which, in particular, is designed to be telescopically resilient in a fluidic, that is to say pneumatic or hydraulic way, or which has a mechanical spring element such as a helical spring.
In order to prevent an overload event in due time even before this state is reached, the centrifuge has a torque determiner for determining the instantaneous torque load upon the cylinder/piston unit. These devices can, for example, determine the length variation of the overload lever arm and/or determine the relative or absolute variation in the tilt angle of the piston rod with respect to an initial position. This information can be used to judge what precisely is the prevailing operating state.
Methods which operate by torque overload protection and which shut down the inflow at a first limit value already are known in the prior art. However, by means of the method according to the invention, by overall two limit values being stipulated with a change in the operating parameters taking place when a first limit value is reached or overshot and with a shutdown occurring when a second limit value is reached or overshot, an overload event can be prevented even more reliably. Only when the overload protection is triggered does complicated cleaning of the centrifuge, in particular of the screw, become necessary. This can be prevented, inter alia, by the novel step of timely shutdown.
The use of the method in the processing of drill sludge has proved to be especially expedient since the processing of drill sludge entails the occurrence of unforeseen states which lie outside the normal operation of the centrifuge. Via more differentiated monitoring of the torque with the aid of the stipulation of a first and of a second limit value, the percentage of overload events occurring can be surprisingly reduced.
The invention is explained in more detail below by means of an exemplary embodiment, with reference to the accompanying drawings.